Sanitised in May, by August it smelled of mould again – why so fast?
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Titan, Câmpia Libertății street, 1980 block, 12,000 BTU Samsung, 5 years old, living room with open kitchen. Had it sanitised in May by a company (not sure of the method, they had a cover and washed). By August, mould smell again. They say it is normal. Is it? What did I do wrong?
What is really happening
Biofilm does not start from zero after a partial wash: if colonies remain on the back of the evaporator, inside the roller or in the pan sludge, they repopulate the whole surface within weeks, because they have moisture, temperature and, with an open kitchen, plenty of food. Studies measuring cleaning effectiveness show over 99% reductions only when all components are washed, including the roller – which many companies merely 'spray' because it is hard to reach. Add the habit of switching off wet: a damp evaporator every night is a daily incubator. It is not 'normal' – it is a predictable result of the two.
- A picture can document visible deposits.
- Colour and appearance do not reliably identify microorganisms.
- The appropriate assessment depends on the issue; a photo is not a laboratory test.
- Washing with alkaline detergent, brushing and high-pressure rinsing reduces fungi inside the unit by more than 99%. [Indoor Air, 2023]
- The blower (cross-flow fan) is the most fungus-contaminated component of a split unit, more than the filter or the front of the evaporator. [Indoor Air, 2023]
- Air conditioners in Japanese homes host distinct bacterial communities on each component, showing that every part must be cleaned separately. [CORE (open access repository), 2015]
- Manufacturers recommend running the unit in fan-only mode for several hours to dry the interior before long periods of non-use, precisely to prevent odour and mould. [Daikin Europe, 2020]
What we do on site
- Inspection and photos – we show you exactly where dirt was left from the previous visit, without commenting on the company.
- Collection cover; cleaning solution on evaporator (both faces), roller (inside and out), pan, hose.
- Pressure wash in place; we check the roller by rotating it fully.
- Sanitising solution on everything.
- Outdoor unit, washed in place.
- We leave the drying rule written on a note stuck to the remote. See current rates on the Prices page.
What you can do yourself
- 'Fan' 30 minutes every evening before shut-off – set a timer.
- Hood on with every cooking session; unit off while frying.
- Filters weekly, not fortnightly, as long as the kitchen opens onto the living room.
What NOT to do
- Do not accept 'it is normal' as an answer at 3 months.
- Do not ask for 'indoor only' to save money – a clogged outdoor unit strains the system and changes the condensate regime.
- Do not spray between sanitisings.
Prevention
With all components washed and daily drying, a living-room unit with an open kitchen stays clean a whole season, often two. Annual sanitising, in spring.
When to call us
0764 012 943, Monday–Saturday 08:00–20:00. If the smell returns within 3 months after our visit, we come back free of charge.

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Read also
Sources (6)
- onlinelibrary.wiley.com/doi/10.1155/2023/8984619
- core.ac.uk/works/80197639
- pmc.ncbi.nlm.nih.gov/articles/PMC11350112/
- www.researchgate.net/publication/326930319_Distribution_characteristics_growth_reproductio
- www.daikin-ce.com/content/dam/document-library/operation-manuals/ac/split/ftxf-d/FTXF-D_Op
- web-manual.dit-daikin.com/ra/en/cleaning_filters/
The information on this page is educational and based on cited sources; it does not replace medical advice. We do not do repairs, installation or refrigerant circuit work.